System and method of operation of an embedded system for a digital capacitance diaphragm gauge

ABSTRACT

Systems and methods for digitally controlling sensors. In one embodiment, a digital controller for a capacitance diaphragm gauge is embedded in a digital signal processor (DSP). The controller receives digitized input from a sensor AFE via a variable gain module, a zero offset module and an analog-to-digital converter. The controller automatically calibrates the received input by adjusting the variable gain and zero offset modules. The controller also monitors and adjusts a heater assembly to maintain an appropriate temperature at the sensor. The controller utilizes a kernel module that allocates processing resources to the various tasks of a gauge controller module. The kernel module repetitively executes iterations of a loop, wherein in each iteration, all of a set of high priority tasks are performed and one of a set of lower priority tasks are performed. The controller module thereby provides sensor measurement output at precisely periodic intervals, while performing ancillary functions as well.

BACKGROUND OF INVENTION

[0001] 1. Technical Field of the Invention

[0002] This invention relates generally to the systems and methods foroperation of sensors and more particularly to embedded control systemsfor a digital capacitance diaphragm gauge using an advanced digitalsignal processor, including kernel and gauge control algorithms toprocess internal gauge functions.

[0003] 2. Related Application

[0004] The present application is related to the subject matter of U.S.patent application Ser. No. 09/350,744, filed July 9, 1999.

BACKGROUND OF THE INVENTION

[0005] Many manufacturing processes require accurate and repeatablepressure measurements during critical process steps. These processes mayrely on capacitance diaphragm gauges to achieve an accuratedetermination of process chamber pressure. Capacitance diaphragm gauges(or capacitance manometers) are widely used in the semiconductorindustry. In part, this is because they are typically well suited to thecorrosive services of this industry. They are also favored because oftheir high accuracy and immunity to contamination.

[0006] A capacitance manometer is a type of sensor which may be used tomeasure parameters such as the pressure within a process chamber. Acapacitance manometer has a housing containing two chambers separated bya diaphragm. One of the chambers is in fluid communication with theprocess chamber or conduit in which the pressure is to be measured. Theother chamber of the manometer is a typically (although not necessarily)evacuated. It is a pressure reference chamber. Plates are located on themanometer housing and on the diaphragm. These plates have a capacitancethat can be measured. When the process gas enters the first chamber, itexerts a pressure against the diaphragm and causes the diaphragm tomove. The capacitive plate connected to the diaphragm is consequentlymoved toward the plate connected to the manometer housing, changing thecapacitance between the plates. The change in capacitance corresponds tothe increase in pressure and can be used as a measurement of thepressure.

[0007] Capacitance manometers typically operate by measuring the changein electrical capacitance that results from the relative movement of thesensing electrodes. The change in capacitance can be measured usingvarious different types of electrical interfaces, such as balanced diodebridge interfaces, guarded secondary transformer-based bridgeinterfaces, and matched reference capacitor bridge interfaces. Theseinterfaces measure changes in capacitance, using circuitry coupled tothe capacitive plates of the manometer in order to determine changes intheir capacitance and corresponding changes in the measured parameter.

[0008] One of the major advantages of a capacitance diaphragm gauge isits ability to detect extremely small diaphragm movements, henceextremely small changes in the measured process parameter. The accuracyof these sensors is typically 0.25 to 0.5% of the generated reading. Forexample, in a typical capacitance diaphragm pressure sensor, a thindiaphragm can measure down to 10⁻⁵ Torr. Thicker, but more ruggeddiaphragms can measure in the low vacuum to atmospheric range. To covera wide vacuum range, two or more capacitance sensing heads can beconnected into a multi-range package.

[0009] Systems that utilize differential capacitance manometersgenerally have stringent requirements for the repeatability of pressurereadings, with offset drift typically limited to 0.02% of full scale perday. Full scale deflection for a differential capacitance manometertypically causes capacitance changes of 0.2 2.0 pF (10⁻¹² F). Thus, theelectronic interface (“Analog Front End” or “AFE”) to the sensingelement may not experience drift in excess of 0.04 femtoFarad (10⁻¹⁵ F)per day.

[0010] In addition to stringent performance requirements, customers areincreasingly requiring features that allow differential capacitancemanometer based systems to take advantage of advancements in otherprocess equipment. For example, digital communications, embeddeddiagnostics and lower temperature sensitivity are now required by someof the latest process technologies. Legacy capacitance diaphragm gaugesoften cannot meet these requirements.

SUMMARY OF INVENTION

[0011] One or more of the problems outlined above may be solved by thevarious embodiments of the invention. Broadly speaking, the inventioncomprises systems and methods for digitally controlling sensors. Thevarious embodiments of the invention may substantially reduce oreliminate the disadvantages and issues associated with prior art systemsand methods for operating sensors.

[0012] In one embodiment, a digital controller for a capacitancediaphragm gauge is embedded in a digital signal processor (DSP). Thecontroller receives digitized input from a sensor analog front end via avariable gain module, a zero offset module and an analog-to-digitalconverter (ADC). The controller automatically scales the received inputby adjusting the variable gain and zero offset modules. The controlleralso monitors and adjusts a heater assembly to maintain an appropriatetemperature at the sensor. The controller utilizes a kernel softwaremodule that allocates processing resources to the various tasks of agauge controller module. The kernel module repetitively executesiterations of a loop, wherein in each iteration, all of a set of highpriority tasks are performed and one of a set of lower priority tasksare performed. The controller module thereby provides sensor measurementoutput at precisely periodic intervals, while performing ancillaryfunctions (e.g., automatic scaling, zero offset adjustment and embeddeddiagnostics) as well.

[0013] The present systems and methods may provide a number ofadvantages over the prior art. For example, they may enable thecontroller to simultaneously service the digital tool controllerinterface and the embedded diagnostics port interface. Further, they mayenable embedded diagnostics within the controller. The digital engine ofthe controller can discretely monitor system variables and seamlesslypresent the data to the tool controller and/or the embedded diagnosticsport. System variables may include but are not limited to the gaugepressure, sensor temperature(s), heater drive (s), ambient temperature,preprocessed gauge pressure, zero offset, and device status. Stillfurther, there is no need for potentiometers for manual adjustments inthe present systems and methods. Except for a single gauge balancingresistor manually installed during assembly, all calibration adjustmentsare made digitally by an automated calibration stand. All calibrationparameters are stored in nonvolatile memory and are accessible via theembedded diagnostics port. Still further, the present systems andmethods may enable linearization of the gauge and configuration of thesensor heater controller via the embedded diagnostics port.

BRIEF DESCRIPTION OF DRAWINGS

[0014] Other objects and advantages of the invention may become apparentupon reading the following detailed description and upon reference tothe accompanying drawings.

[0015]FIG. 1 is a hardware block diagram illustrating an embedded systemcontroller in one embodiment.

[0016]FIG. 2 is a flow chart illustrating the operation of the kernelmodule of the embedded system in one embodiment.

[0017]FIG. 3 is a block diagram illustrating the gauge controller moduleof the embedded system in one embodiment.

[0018] While the invention is subject to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and the accompanying detailed description. Itshould be understood, however, that the drawings and detaileddescription are not intended to limit the invention to the particularembodiment which is described. This disclosure is instead intended tocover all modifications, equivalents and alternatives falling within thescope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION

[0019] Overview

[0020] A preferred embodiment of the invention is described below. Itshould be noted that this and any other embodiments described below areexemplary and are intended to be illustrative of the invention ratherthan limiting.

[0021] Broadly speaking, the invention comprises systems and methods fordigitally controlling sensors. The various embodiments of the inventionmay substantially reduce or eliminate the disadvantages and issuesassociated with prior art systems and methods for operating sensors.

[0022] In one embodiment, a digital controller for a capacitancediaphragm gauge is embedded in a digital signal processor (DSP). Thecontroller receives digitized input from a sensor AFE via a variablegain module, a zero offset module and an analog-to-digital converter(ADC). The controller automatically scales the received input byadjusting the variable gain and zero offset modules. The controller alsomonitors and adjusts a heater assembly to maintain an appropriatetemperature at the sensor.

[0023] The controller utilizes a kernel module that allocates processingresources to the various tasks of a gauge controller module. The kernelmodule repetitively executes iterations of a loop, wherein in eachiteration, all of a set of high priority tasks are performed and one ofa set of lower priority tasks is performed. In one embodiment, the highpriority tasks comprise reading the digitized input from the sensor,linearizing the input, and providing a pressure output. The lowerpriority tasks comprise servicing serial communication interface (SCI)messages, servicing control area network (CAN) messages, compensatingfor ambient temperature, controlling the sensor heater, controllingtemperature and status LEDs, checking for zero pressure and overpressureand the like.

[0024] The digital engine of the controller monitors system variablesfor the purpose of producing accurate, repeatable, and temperaturecompensated pressure output, while simultaneously supporting a digitaltool controller interface, an independent diagnostics interface, aclosed loop heater controller and other gauge functionality. All ofthese functions are executed without affecting the accuracy orperformance of the gauge

[0025] Advantages. In order to meet many of the new requirements fordifferential capacitance manometer systems, a digital control system maybe required. Traditional analog signals are susceptible to noise, groundloops, and signal loss. These issues can be resolved with digitalcommunications, due to their immunity to noise and signal degradation.In one embodiment, a digital communication interface on the gauge isimplemented using an embedded digital control system.

[0026] The prior art provides few, if any, diagnostic features.Traditional analog gauges must be removed from the tool to be diagnosed.Using the present systems and methods, the gauges need not be removed inorder to diagnose or resolve problems. Internal system parameters may bemonitored or retrieved during normal operation through, for example, adigital diagnostics port, or an interface to a PC, notebook computer,PDA or calibration stand. The gauges may also include embeddeddiagnostics to facilitate resolution of tool or gauge problems. Suchfeatures may reduce the cost of ownership by allowing tool or sensorissues to be quickly identified and resolved.

[0027] Conventional analog gauges are calibrated by adjusting a numberof potentiometers through a process that is primarily one of manualcalibration. The present systems and methods, however, may provide forautomatic calibration (e.g., by an automated calibration stand). In oneembodiment, an embedded digital engine enables automated calibration andtesting, which lowers the cost of manufacturing and reduces variabilityfrom device to device. No potentiometers are required, in contrast tothe prior art. Since calibration is done digitally and automatically,there is much less chance of human induced variability. Higher levels ofaccuracy, repeatability, and device-to-device reproducibility aretherefore possible.

[0028] High performance capacitance diaphragm gauges are typicallysubject to temperature coefficient requirements. That is, thesensitivity of the gauges to temperature variations should be minimal.Reducing temperature coefficient values generally requires a precisionsensor heater control system. Advanced heater control is alsofacilitated by the present systems and methods, which use digitaltechniques to monitor and control heater output. The present systems andmethods also utilize measurements of ambient temperature to compensatefor variations in the temperature of the electronic circuit.

[0029] The present systems and methods therefore provide high levels ofgauge performance, while enabling simultaneous digital communicationswith host equipment and diagnostics facilities. Furthermore, the presentsystems and methods may reduce the cost of manufacturing of the gaugesand the cost of ownership of the end user.

[0030] Preferred Embodiment.

[0031] Referring to FIG. 1, a functional block diagram illustrating thestructure of a sensor system having a digital controller is shown. Inthe embodiment depicted in this figure, a controller is implemented in adigital signal processor (DSP) 110. In other embodiments, the controllermay be implemented in a microcontroller or other data processor. Thecontroller receives digitized input from the sensor 10, processes theinput, controls the sensor and related components, performs variousservice functions and provides output data to a user. In one embodiment,the controller DSP is embedded in (integral with) the sensor.

[0032] Pressure Acquisition. In this embodiment, a signal from thesensor (e.g., capacitance diaphragm gauge) 10 is converted to a voltageby the Analog Front End (AFE) 30. The AFE signal is then amplified by aprogrammable gain amplifier 40 and zero adjusted by a zero offset module50. Both programmable gain amplifier 40 and zero offset module 50 arecontrolled by the embedded controller, DSP 110. The amplified and offsetanalog signal is then converted to a digital signal by analog-to-digitalconverter (ADC) 60. ADC 60 then communicates the digital signal to theprocessor upon command from the embedded control code.

[0033] Programmable gain amplifier 40 and zero offset module 50 are usedto modify the signal generated by AFE 30 because sensor outputs can varysignificantly from one sensor to another. The signal is thereforeautomatically adjusted to appropriate levels prior to digitization.These components replace the potentiometers used in prior art systemsfor gain and offset adjustments. By eliminating the potentiometers,which are susceptible to incorrect adjustment and which typically havehigh temperature coefficients, gauge performance is improved.

[0034] Signal Processing. The digitized pressure signal received by DSP110 is processed using digital techniques to convert the nonlinearsensor signal to a linear pressure signal. This process employs alinearization algorithm that is based on constants computed during theautomatic calibration of the controller. These constants are maintainedin non-volatile memory in the EEPROM 150. A temperature compensationalgorithm is also used to process the signal to compensate fortemperature variations in the electronics.

[0035] After the digital signal is processed by the DSP, it can be sentto one or more output ports. The digital signal can be transmitteddirectly to a digital device or network, such as control area network(CAN) transceiver 101, which can then make it available to a DeviceNetnetwork 102, or an RS232/485 embedded diagnostics port, through which itcan be made available to a calibration stand, PC, or other devices. Theprocessed digital signal may also be sent to a digital-to-analogconverter (DAC) 70 to produce an analog signal suitable for an analogdevice. The analog signal may be scaled by circuit 103 and linearized byan algorithm if necessary prior to being conveyed to the device 104.

[0036] Zero Offset. The zero offset is the output of the gauge when itis exposed to a base pressure or a pressure which is below the detectionresolution of the gauge. One of the problems with conventional CDGs iscontrol of zero offset drift in the gauge. Most gauges will experiencesome drift or shifting of the zero offset value over time. The gaugestherefore need to be periodically adjusted to compensate for the drift.Conventional gauges require that a user (e.g., a technician) adjust apotentiometer until the gauge output shows zero volts when it is exposedto base pressure.

[0037] The present systems and methods simplify this zero adjustprocedure by eliminating the adjustment potentiometer. The controller isconfigured to monitor the pressure signal and automatically adjust zerooffset module 50 in response to an appropriate command. Because theadjustment of the zero offset is automatically performed by thecontroller, the time required to adjust the zero offset is minimized.There is also a reduced risk of incorrect adjustment because theopportunity for human error in adjustment of a potentiometer iseliminated. (It should also be noted that the accuracy of the adjustmentis typically substantially greater than can be obtained by manualadjustment of a potentiometer.) The zero adjust procedure may be invokedmanually (e.g., by a user pressing a button) or it may be initiated inresponse to a signal from the tool port, the diagnostics port, contactclosure, or even the controller itself.

[0038] In one embodiment, the controller incorporates a lock out featurerelating to the zero adjust procedure. Adjustment of the zero offsetshould only be performed when the appropriate conditions exist. If oneof these conditions is not met, error may be introduced into thesubsequent measurements. In one embodiment, the following conditionsshould be met before a zero adjust procedure is performed: the inletpressure should be below the zero adjust limit of the gauge; the sensorshould be at the set point temperature; the ambient temperature of theelectronics should be within a predetermined range; an overpressuresignal should not be asserted; and no fault conditions should existwithin the sensor or controller. Because failure to observe theseconditions may result in improper adjustment, the controller isconfigured to prevent the zero adjustment from taking place unless theseconditions are met.

[0039] Variable gain. The controller may also provide for automaticcalibration of the system. Because the sensor signal may not have theoptimal signal range (i.e., magnitude and displacement from zero), it isat times necessary to adjust the variable gain module, as well as thezero offset module, to obtain the best possible signal to input to theanalog-to-digital converter and controller. The controller is configuredto provide control inputs to the variable gain and zero offset modulesand thereby adjust them. This eliminates the need to manually adjustpotentiometers as in conventional systems. By adjusting these modulesbased on the digitized sensor signal, the accuracy and repeatability ofthe calibration is improved.

[0040] Heater Control. In this embodiment, the controller is alsoresponsible for controlling the sensor heater assembly 20. The heaterassembly is necessary in this embodiment because the sensor output is afunction of temperature, and because sensor performance may be affectedby the condensation of process gasses on the diaphragm of the sensor (acapacitance diaphragm gauge). The controller therefore monitors thetemperature of the sensor and adjusts the temperature of the heaterassembly to maintain the desired set point temperature at the sensor.The control of the heater is implemented in a closed loop subsystemwhich is operated in parallel with other system functions and which doesnot degrade gauge accuracy or performance.

[0041] Ambient Temperature Compensation. Ambient temperature also has aneffect on the performance of the sensor, although it is generally lessthan the effect of sensor temperature. The controller is thereforecoupled to an ambient temperature sensor 140. The controller receivesambient temperature information from sensor 140 and processes thedigital signal to compensate for the effects of ambient temperature.

[0042] Digital Communications Ports. As noted above, the controller canprovide the processed digital signal to a number of ports for use byvarious other devices. For instance, the controller may have a CANinterface for sending data to CAN transceiver 101, which can then sendthe data to a DeviceNet network. The controller likewise has a pressureoutput port coupled to DAC 70, which can provide an analog signal(corresponding to the digital signal) to external analog devices. Stillfurther, the controller can send the data via a UART (universalasynchronous receiver/transmitter) to an RS232/485 diagnostics port 100.Diagnostics port 100 is independent and is available to enable automaticcalibration, testing, and troubleshooting features of the controller.This port enables the controller to provide diagnostic data via a seriallink to a PC, laptop, PDA, calibration stand or the like (105). Thediagnostics port may also enable remote diagnostics if it is interfacedwith an appropriate web server device.

[0043] Other Hardware Modules. Other signals monitored by the controllerin this embodiment include the address, baud rate selector and MacIDswitches (160), and various status (e.g., fault) and temperature LEDs(170). The status and temperature LEDs may be driven by embeddeddiagnostics in the controller. The controller also interfaces with anon-volatile memory (e.g., EEPROM 150) to store calibration andconfiguration parameters. These hardware features are discussed in moredetail elsewhere in this disclosure.

[0044] Software. The DSP in which the controller is implemented isprogrammed to periodically execute certain tasks, including thefunctional tasks involved in processing sensor signals and the ancillarytasks involved in the diagnostic, calibration and other non-measurementfunctions. This programming is implemented in one embodiment by a kernelmodule and a controller module. The kernel module executes continuallyand allocates processing resources to the various tasks that are to beperformed, while the controller module actually performs the tasks.

[0045] Kernel Module. As noted above, the kernel in this embodiment ofthe embedded controller allocates processor resources to the individualtasks of the controller module. Because the primary purpose of theembedded controller is to control a sensor, the first priority of thecontroller is to service the sensing functions of the system. The kernelis designed to provide precisely periodic service of these functions. Inthis embodiment, these functions include reading the digitized pressuresignal from the analog-to-digital converter, linearizing the digitizedpressure signal and providing the linearized signal to the variousoutput ports (particularly those intended specifically for sensoroutput). By allocating resources to these high priority tasks first, thekernel ensures timely and accurate determination of the sensed pressure.

[0046] Since the embedded controller in this embodiment is used in aclosed loop pressure control system, it is important that the controllerdoes not induce any variations in its pressure response time. If thefunctions relating to the processing of the pressure signal weredelayed, the pressure control system would effectively be operating withstale data and would produce potentially erroneous control data. Thekernel therefore allocates processor resources to the lower prioritytasks in such a way as not to delay or interrupt the high prioritypressure calculation tasks.

[0047] The kernel is paced by a timer which periodically generatesinterrupts that trigger the high priority pressure calculation tasks.Each interrupt triggers a new iteration of a control flow that includesexecution of all of the high priority tasks and, in this embodiment, oneof the lower priority tasks. Each high priority task completes executionprior to the next timer interrupt. The remainder of the time before thenext interrupt can be used for the lower priority tasks.

[0048] In one embodiment, the high priority tasks include: reading theAFE output from the analog-to-digital converter; calculating thelinearized pressure output; writing the linearized pressure value to theDAC(s); servicing CAN buffers; and servicing serial port buffers.

[0049] The lower priority tasks in this embodiment include: processingserial communication messages (via embedded diagnostics port 100);processing CAN messages (via DeviceNet port 101); updating ambienttemperature compensation; servicing closed loop heater algorithm;servicing temperature LEDs; monitoring overpressure and zero adjustinputs; servicing status LEDs 170 and switches 160; and servicing EEPROM150.

[0050] Referring to FIG. 2, a flow diagram illustrating the operation ofthe embedded system kernel is shown. Upon power-up (or a reset event),the kernel allocates resources to the initialization of the DSP,including the controller module and the kernel module itself. Afterinitialization is complete, the kernel repetitively executes loop 200,which consists generally of steps 220 and 230. Each iteration of thisloop is executed in response to a signal from timer 210, ensuring thatthe loop is executed in a precisely periodic manner.

[0051] Step 220 comprises the tasks that are involved in the processingof sensor output to generate an output signal (i.e., the high prioritytasks). In the embodiment described above, these tasks comprise readingthe digital signal produced by analog to digital converter 60,linearizing this signal to produce a linear pressure output signal,performing temperature compensation adjustment of the pressure signaland writing the resulting pressure data to the buffers out of thedigital to analog converter, CAN and diagnostic (SCI) ports. Each ofthese tasks is executed once in every iteration of the loop. Themeasurement function of the sensor controller system therefore has thesame periodicity as timer 210.

[0052] After the high priority tasks of step 220 are performed, one ofthe lower priority tasks is selected in step 230. Each of these tasks isshown in the figure as a separate step (240-247). In the embodimentdepicted in the figure, the lower priority tasks comprise: servicing SCImessages (240); servicing CAN messages (241); performing temperaturecompensation (242); performing heater control (243); controllingtemperature LEDs (244); performing zero and overpressure checks (245);controlling status LEDs (246); and controlling EEPROM and elapsed-timetimers (247). The lower priority task to be executed in a giveniteration of the loop is selected based upon a task counter that isincremented upon completion of the lower priority task in each loop (seestep 250). Consequently, the lower priority tasks of steps 240-247 areexecuted sequentially, one per iteration of loop 200. Put another way,each low priority task is serviced every “N” timer iterations, where “N”is the number of tasks in the task list.

[0053] In this embodiment, the timer 210 that controls the initiation ofeach iteration of loop 200 is a set to allow sufficient time forcompletion of all of the high priority tasks and any one of the lowerpriority tasks (as well as the incrementing of the task counter). Inother embodiments, it may be desirable to shorten the timer cycle toprovide more frequent updates of the sensor output reading generated bythe controller. In this instance, there may not be sufficient time tocomplete the selected lower priority task. Provisions may therefore bemade in the design to allow for incomplete execution of a selected taskand resumption or re-execution of the task at a later time.Alternatively, it may not be necessary to frequently update the sensoroutput reading of the controller. In this instance, it may be possibleto increase the interval of the timer so that more than one of the lowerpriority tasks can be completed in a single iteration of the loop. Othervariations may also be possible.

[0054] Using the kernel control loop shown in FIG. 2, each taskcompletes before the next timer interrupt occurs. This sequentialprocess ensures that the gauge control system is able to read,linearize, and output chamber pressure in a precisely periodic mannerwhile also servicing all other gauge functions. This control floweffectively prioritizes computational resources for the purpose ofmaximizing gauge accuracy and performance, while still providingancillary functions.

[0055] Controller Module. As mentioned above, the controller moduleexecutes the tasks of the embedded controller as resources are allocatedby the kernel. The structure of the controller module is shown in FIG.3. The structure is described below with reference to the figure.

[0056] In one embodiment, the controller module software is programmedinto a DSP. (It should be noted that “software” as used here refers to aset of program instructions configured to cause the DSP to perform adesignated task, and is intended to include software, firmware andhard-coded instructions.) The controller module is configured to receivedata from the heater assembly and sensor, the AFE and theanalog-to-digital converter. The controller module also receives controlinput from the zero button (when a user pushes the button to initiatethe automatic re-zeroing process). The controller module provides outputdata in this embodiment to the CAN port, the digital-to-analog converterand the diagnostics port (RS232/485). The controller module providescontrol output to the analog zero offset and gain components, as well asthe heater assembly and sensor.

[0057] Controller module 300 includes a heater controller module 310that is configured to receive temperature data from temperature sensorscoupled to sensor 10. Heater controller module 310 processes this datato determine whether the temperature of sensor 10 is appropriate and toadjust the temperature if necessary. This may involve separatelycontrolling multiple heating components corresponding to different zonesof sensor 10. Heater set point and tuning values are stored in theEEPROM and are restored on power-up.

[0058] Zero adjust module 330 is configured to initiate the zero offsetadjustment procedure in response to a signal received from the zerobutton. Zero adjust module 330 automatically determines the drift of thesensor and/or analog front end so that it can be corrected. In otherwords, zero adjust module 330 determines the adjustment necessary tocause the sensor signal digitized by the analog-to-digital converter tobe zero when the pressure is effectively zero (i.e., below a minimumresolvable pressure.) This information can then be sent to a zero offsetcontrol module, which in turn causes the actual adjustment of the zerooffset hardware module. The adjustment is stored in the EEPRPOM and isrestored on power up.

[0059] It should be noted that, in one embodiment, zero adjust module330 incorporates a lock out feature. This prevents zero offsetadjustment if the appropriate conditions for the adjustment (those forwhich the adjustment can be properly executed) are not met. In otherwords, the automatic zero offset adjustment procedure is locked out. Thespecific conditions that must be met in this embodiment are that thepressure at the sensor is below a predetermined threshold, the sensortemperature is at the desired setpoint, the ambient temperature of theelectronics is within a predetermined range, and no fault conditions arepresent in the controller.

[0060] EEPROM module 320 is configured to manage the storage of data inthe EEPROM (electronically erasable programmable read only memory). TheEEPROM module stores gain and zero adjust values, configuration data,historical diagnostic data, and heater configuration and control data.As noted above, the linearization constants that are computed bycontroller module 300 are also stored in the EEPROM. These constants areused by pressure linearization module 340 to convert the non-lineardigitized signal received from the analog-to-digital converter into alinear pressure signal that can be output through the appropriate ports.It should be noted that the linear pressure signal produced by pressurelinearization module 340 may have to be processed by temperaturecompensation module 350 in order to correct for changes in ambienttemperature.

[0061] Once the pressure signal is linearized and temperaturecompensated, it can be sent to the appropriate output modules. In oneembodiment, these modules include a tool controller module 360 that isconfigured to control output to a CAN port (which may be made availableto a DeviceNet network), an embedded diagnostics and calibration module370 that is configured to control output to the dedicated diagnosticsport, and a digital-to-analog converter module 380 that is configured tocontrol output to the digital-to-analog converter.

[0062] Embedded diagnostics and calibration module 370 enablescommunication between the controller module and an external device suchas a calibration stand or a PC. The controller can therefore performdiagnostic procedures using the digital signal data and internalcontroller data and then communicate this information to a user. Itshould be noted that the particular diagnostics performed may vary fromone embodiment to another, so no specific procedures will be discussedhere. The programming of particular procedures is believed to be withinthe abilities of a person of ordinary skill in the art of the invention.The diagnostics may produce indications of fault conditions, which mayin turn be communicated to a user, used to drive LED indicators, usedfor other diagnostic procedures and so on. In one embodiment, the faultconditions are recorded in a historical database for later analysis.

[0063] The calibration performed by embedded diagnostics and calibrationmodule 370 also utilizes communications from an external device, i.e., acalibration stand. The module is configured to receive data downloadedfrom the calibration stand, such as calibration constants or other datadescribing the multivariable response function utilized in the automaticcalibration procedures. This information can then be used, along withinternal variables such as the unprocessed sensor signal, the ambienttemperature, sensor temperature and the overpressure signal, to adjustthe variable gain and zero offset hardware modules to obtain optimizedinput data.

[0064] It can be seen from FIG. 3 that, in addition to the zero offsetcontrol module which controls the offset of the analog sensor signal,controller module 300 includes a sensor gain control module. This modulecontrols the programmable gain hardware module that amplifies the analogsensor signal from the analog front end. This allows the mostappropriate signal level to be provided to the input of theanalog-to-digital converter. Both the amplifier gain and zero adjustvalues are stored in EEPROM and are restored at power up. Controllermodule 300 additionally includes an overpressure input module that isconfigured to sense an overpressure condition in the analog front end.

[0065] In addition to the embodiments of the invention described above,there are various alternative embodiments that are within the scope ofthe present disclosure. For example, one alternative embodiment maycomprise a sensor system having a sensor, an analog front end, ananalog-to-digital converter and a digital controller, as describedabove. This system may include other hardware components, alone or incombination. These components may include a sensor heater, a variablegain module, a zero offset module, a memory (e.g., an EEPROM),communication ports, calibration stands, PCs, PDAs, networks, or otherexternal equipment.

[0066] Other embodiments may comprise methods. For example, onealternative embodiment comprises a method for performing a zeroadjustment. This method includes the following steps: detecting a zeroadjust command (e.g., from a user pushbutton switch, a contact closure,or a digital command from a communication ports); sensing the zerooffset value of the inlet pressure signal; digitally removing the zerooffset signal from the linearized pressure output signal; and updatingthe zero adjust status variable. This method may further include thesteps of indicating the success or failure of the zero adjust operation,performing the procedure only if predetermined conditions are met(otherwise locking out the procedure), and so on.

[0067] Yet another alternative embodiment may comprise a method forcalibrating a sensor such as a capacitance diaphragm gauge. The steps ofthis method may comprise: measuring the actual pressure at the sensorinlet; sensing a series of system variables associated with thecapacitance diaphragm gauge (e.g., unprocessed input pressure signal,ambient temperature signal, sensor temperature signals or overpressuresignal); controlling another series of system variables associated withthe capacitance diaphragm gauge (e.g., sensor gain amplifier value orzero offset value); modeling the pressure with a regression technique toproduce a multivariable response function describing the gauge pressurein terms of the system variables; and inputting the multivariableresponse function into an embedded control system to enable the outputof a pressure signal.

[0068] The benefits and advantages which may be provided by the presentinvention have been described above with regard to specific embodiments.These benefits and advantages, and any elements or limitations that maycause them to occur or to become more pronounced are not to be construedas a critical, required, or essential features of any or all of theclaims. As used herein, the terms “comprises,” “comprising,” or anyother variations thereof, are intended to be interpreted asnonexclusively including the elements or limitations which follow thoseterms. Accordingly, a process, method, article, or apparatus thatcomprises a list of elements does not include only those elements butmay include other elements not expressly listed or inherent to theclaimed process, method, article, or apparatus.

[0069] While the present invention has been described with reference toparticular embodiments, it should be understood that the embodiments areillustrative and that the scope of the invention is not limited to theseembodiments. Many variations, modifications, additions and improvementsto the embodiments described above are possible. It is contemplated thatthese variations, modifications, additions and improvements fall withinthe scope of the invention as detailed within the following claims.

1. A digitally controlled sensor system comprising: a sensor; an analogfront end module coupled to the sensor and configured to produce ananalog sensor signal; an analog-to-digital converter configured toconvert the analog sensor signal to a digital sensor signal; and adigital controller configured to receive the digital sensor signal,process the signal and provide an output signal indicating a measuredparameter corresponding to the sensor signal.
 2. The system of claim 1,wherein the digital controller is implemented in a digital signalprocessor (DSP) and wherein the DSP is embedded in the sensor.
 3. Thesystem of claim 1, wherein the digital controller is implemented in amicrocontroller and wherein the microcontroller is embedded in thesensor.
 4. The system of claim 1, wherein the sensor comprises a digitalcapacitance gauge.
 5. The system of claim 1, wherein the controllerutilizes a kernel module which is configured to perform iterations of acontrol loop, wherein the control loop comprises execution of all of aset of high priority tasks and execution of one or more low prioritytasks.
 6. The system of claim 5, wherein each iteration of the controlloop is performed at a periodic time.
 7. The system of claim 5, whereinthe high priority tasks comprise at least one or more of the groupconsisting of: reading the digital sensor signal from theanalog-to-digital converter; calculating a linearized pressure valuefrom the digital sensor signal; writing the linearized pressure value toa digital-to-analog converter; and conveying the linearized pressurevalue to one or more port buffers.
 8. The system of claim 5, wherein thelow priority tasks comprise at least one or more of the group consistingof: processing communication messages received from a diagnostics port;processing control area network messages; performing ambient temperaturecompensation; performing a closed loop heater algorithm; servicingtemperature LEDs; monitoring overpressure and zero adjust inputs;servicing status LEDs and switches; servicing an EEPROM; performing anautomatic analog scaling procedure; performing an automatic zero adjustprocedure; and performing an embedded diagnostic procedure.
 9. Thesystem of claim 1, wherein the digital controller is configured toperform an automatic calibration procedure.
 10. The system of claim 1,wherein the digital controller is configured to compute a set ofcalibration constants upon which linearization calculations are based.11. The system of claim 10, wherein the digital controller is configuredto compute the set of calibration constants using a regressionprocedure.
 12. The system of claim 10, wherein the digital controller isconfigured to archive the set of calibration constants in a non-volatilememory.
 13. The system of claim 9, wherein the digital controller isconfigured to perform the automatic calibration procedure usingcalibration data imported to the digital controller from a calibrationstand.
 14. The system of claim 1, wherein the digital controller isconfigured to perform an automatic zero adjust procedure.
 15. The systemof claim 14, wherein the digital controller is configured to perform theautomatic zero adjust procedure in response to an indication from auser.
 16. The system of claim 14, wherein the digital controller isconfigured to perform the automatic zero adjust procedure in response toan electronic indication received via a network connection.
 17. Thesystem of claim 14, wherein the digital controller is configured toprovide control data to an analog zero adjust module, wherein thecontrol data is generated by the automatic zero adjust procedure. 18.The system of claim 14, wherein the digital controller is configured tolock out the automatic zero adjust procedure unless a predetermined setof conditions is met.
 19. The system of claim 18, wherein thepredetermined set of conditions include one or more of the groupconsisting of: inlet pressure being below a detection limit of thesensor; the sensor and its electronics being at a set point temperature;ambient temperature being within a predetermined range; an overpressuresignal not being asserted; and no fault conditions existing within thesensor or controller.
 20. The system of claim 1, wherein the digitalcontroller is configured to perform one or more embedded diagnosticprocedures.
 21. The system of claim 20, wherein the digital controlleris configured to provide an indication of a fault condition detected bythe one or more embedded diagnostic procedures.
 22. The system of claim20, wherein the digital controller is configured to archive detectedfault conditions.
 23. The system of claim 1, wherein the digitalcontroller is configured to transmit diagnostic data resulting from theone or more embedded diagnostic procedures to a diagnostic port.
 24. Thesystem of claim 1, wherein the digital controller further comprises adedicated diagnostics port.
 25. The system of claim 24, wherein internaldata stored in the digital controller is accessible to external devices.26. The system of claim 1, wherein the digital controller is configuredto linearize the digital sensor signal.
 27. The system of claim 26,wherein the digital controller is configured to linearize the digitalsensor signal using linearization expressions based on values stored ina non-volatile memory.
 28. The system of claim 27, wherein thenon-volatile memory is an EEPROM.
 29. The system of claim 1, wherein thedigital controller is configured to temperature compensate the digitalsensor signal.
 30. A method for digitally controlling a sensor systemcomprising: receiving an analog sensor signal; converting the analogsensor signal to a digital sensor signal; and processing the signal toprovide an output signal indicating a measured parameter correspondingto the sensor signal.
 31. The method of claim 30, wherein the method isimplemented in a digital signal processor (DSP) and wherein the DSP isembedded in the sensor.
 32. The method of claim 30, wherein the methodis implemented in a microcontroller and wherein the microcontroller isembedded in the sensor.
 33. The method of claim 30, further comprisingproducing the sensor signal using a digital capacitance gauge.
 34. Themethod of claim 30, further comprising performing iterations of acontrol loop in a kernel module, wherein the control loop comprisesexecution of all of a set of high priority tasks and execution of one ormore low priority tasks.
 35. The method of claim 34, further comprisingperforming each iteration of the control loop at a periodic time. 36.The method of claim 34, wherein the high priority tasks comprise atleast one or more of the group consisting of: reading the digital sensorsignal from the analog-to-digital converter; calculating a linearizedpressure value from the digital sensor signal; writing the linearizedpressure value to a digital-to-analog converter; and conveying thelinearized pressure value to one or more port buffers.
 37. The method ofclaim 34, wherein the low priority tasks comprise at least one or moreof the group consisting of: processing communication messages receivedfrom a diagnostics port; processing control area network messages;performing ambient temperature compensation; performing a closed loopheater algorithm; servicing temperature LEDs; monitoring overpressureand zero adjust inputs; servicing status LEDs and switches; servicing anEEPROM; performing an automatic analog scaling procedure; performing anautomatic zero adjust procedure; and performing an embedded diagnosticprocedure.
 38. The method of claim 30, further comprising performing anautomatic calibration procedure.
 39. The method of claim 38, whereinperforming the automatic calibration procedure comprises computing a setof calibration constants upon which linearization calculations arebased.
 40. The method of claim 38, wherein computing the set ofcalibration constants is performed using a regression procedure.
 41. Themethod of claim 38, further comprising archiving the set of calibrationconstants in a non-volatile memory.
 42. The method of claim 38, furthercomprising performing the automatic calibration procedure usingcalibration data imported from a calibration stand.
 43. The method ofclaim 30, further comprising performing an automatic zero adjustprocedure.
 44. The method of claim 43, further comprising controlling ananalog zero adjust module according to control data generated by theautomatic zero adjust procedure.
 45. The method of claim 43, furthercomprising locking out the automatic zero adjust procedure unless apredetermined set of conditions is met.
 46. The method of claim 45,wherein the predetermined set of conditions include one or more of thegroup consisting of: inlet pressure being below a zero adjust limit ofthe sensor; the sensor being at a set point temperature; ambienttemperature of the electronics being within a predetermined range; anoverpressure signal not being asserted; and no fault conditions existingwithin the sensor or controller.
 47. The method of claim 30, furthercomprising performing one or more embedded diagnostic procedures. 48.The method of claim 47, further comprising providing an indication of afault condition detected by the one or more embedded diagnosticprocedures.
 49. The method of claim 47, further comprising archivingdetected fault conditions.
 50. The method of claim 30, furthercomprising transmitting diagnostic data resulting from the one or moreembedded diagnostic procedures to a diagnostic port.
 51. The method ofclaim 30, further comprising linearizing the digital sensor signal. 52.The method of claim 51, wherein the digital sensor signal is linearizedusing linearization expressions based on values stored in a non-volatilememory.
 53. The method of claim 52, wherein the non-volatile memory isan EEPROM.
 54. The method of claim 30, further comprising temperaturecompensating the digital sensor signal.